I particularly enjoyed this anime although many others say that the ending is pretty messed up. Honestly, I think the ending is what makes it most exciting.
The story is rather interesting, about cheating and how a simple affair can easily change someone's life completely. I'm sure everyone knows that the ending is a bit different from the rest of the series, but that is not a bad thing, not at all. If it hadan't ended the way it did, I would probably say right now that School Days was about a boy who liked to mess around with all the girls in his school, breaking their hearts. Boring. I'm honestly thankful for the gore ending that changed the dull atmosphere right away.
The characters are ok. They carry a large variety of feelings and they are very very expressive. Each character is different in its own way so I can say that the anime includes all the types of classic anime characters.
I rated School Days 9/10 because there were a few less interesting episodes, so I didn't actually get bored. I find it amazing to watch an anime about the every day life of some school students and don't get bored.